Vinyl chloride-based resins are widely used for a molding material and the like using the characteristics thereof, but have various problems relating to the processing. For example, the thermal decomposition temperature is close to the processing temperature and flowability is insufficient. To overcome these problems, various techniques are known. The main techniques include a method of copolymerizing another monomer with vinyl chloride and a method of mixing a plasticizer or another resin-like substance with a vinyl chloride-based resin.
However, these methods are disadvantageous in that the above problems relating to the processing cannot be solved while the excellent physical and chemical properties peculiar to vinyl chloride-based resins are maintained. For example, when a plasticizer is added or another monomer is copolymerized with vinyl chloride, the mechanical strength of the resulting moldings disadvantageously decreases. On the other hand, in the method of mixing another resin-like substance, in most cases, the processability is apparently improved by decreasing the melt viscosity of the resin. However, because of unsatisfactory compatibility with the vinyl chloride-based resin, gelation is insufficient, resulting in a degradation of mechanical properties and transparency of the resulting moldings.
To overcome these problems, a method in which a (meth)acrylic polymer mainly composed of methyl methacrylate is mixed as a processability modifier in order to accelerate the gelation during mold processing of a vinyl chloride-based resin and improve the appearance of the resulting moldings is proposed (for example, refer to Patent Documents 1 and 2). According to this method, moldings of a vinyl chloride-based resin having high degree of gelation can be produced without degrading the characteristics of the vinyl chloride-based resin. Thus, the processability can be improved while mechanical properties and transparency of the moldings are maintained. Furthermore, it is known that the breaking elongation at high temperatures is improved; thereby the resin can be applied to not only deep-draw molding but also vacuum forming and profile extrusion.
However, in the case where the (meth)acrylic polymer is mixed as a processability modifier, under some mixing conditions and molding conditions, further improvement in the above characteristics is desired. For example, when the vinyl chloride-based resin composition is molded to the shape of the die by profile extrusion or injection molding, the mechanical properties can be improved by increasing the degree of gelation of the vinyl chloride-based resin. However, because of high elastic recovering force, sink and warping are generated in moldings, resulting in the degradation of the commercial value of the moldings. In addition, when the vinyl chloride-based resin composition is formed into a sheet by calendering or the like, the occurrence of air marks can be suppressed but flow marks are generated on the surface of the sheet, resulting in the degradation of the commercial value of the molded articles.
As described above, under the present situation, the improvement of physical properties, for example, further improvement of processability is desired in vinyl chloride-based resin compositions.    [Patent Document 1] Japanese Examined Patent Application Publication No. 52-1746    [Patent Document 2] Japanese Examined Patent Application Publication No. 53-2898